Sympathetic skin response in myelopathies

Autonomic dysfunctions cause significant morbidity and mortality among patients with spinal cord disorders. Sympathetic skin response (SSR), a simple, noninvasive electrophysiological technique, may be useful for assessing sympathetic functions in patients with myelopathies. Our aim was to study SSR in patients with myelopathy and correlate it with clinical features, severity of the impairment, somatosensory evoked potentials, and outcome. Thirty patients (15 men, 15 women) 12 to 60 years old with myelopathies of different etiology were studied. Subjects with clinical, electrophysiologic, or radiologic evidence of lesions outside the spinal cord were excluded. Somatosensory evoked potentials (SSEP) were recorded from scalp with median nerve stimulation at the wrist and posterior tibial nerve below the medial malleolus. The SSR was recorded from palm and sole after stimulating the supraorbital nerve at forehead, median nerve at wrist, and posterior tibial nerve below medial malleolus. The SSR was considered abnormal when absent. The sites of the lesions in these patients were cervical (13), thoracic (16), and lumbar (1). The lesion was clinically complete in six patients. Good motor recovery was noted in 16 subjects. SSR was absent from sole in 25 and palm in 10 patients from all three sites of stimulation. In addition, three patients also had absent SSR from palm on posterior tibial nerve (PTN) stimulation. SSEP was absent from median (N₁₉ in three and posterior tibial (N₃₉) in 20 patients. Among 10 patients with absent SSR from palm, only three had a good outcome. Presence of SSR from palm to PTN stimulation correlated with sparing of bladder sensations and good outcome. However, absent SSR from sole did not correlate with clinical features, bladder dysfunction, or outcome. Sympathetic skin response is frequently abnormal in patients with myelopathies. Spinal afferent and efferent tracts for SSR are different and may be affected individually. The afferent pathways are closely related to tracts conveying bladder sensation. Preserved palmar SSR on PTN stimulation may suggest good motor outcome. SSR may be a valuable adjunct in evaluating patients with myelopathies.